A crowd gathered at the bandstand in Priory Park, in Archie’s home town of Southend, Essex, on Sunday.
People held purple balloons with “forever in our hearts” written on them.
Cards with the message “a mother’s love”, and a photo of Archie and his mother, Hollie Dance, were hung from a pine tree.
Children played with bubbles as music played from speakers in the background.
One person lit a purple flare, holding it in the air as a mark of respect.
Addressing the gathering, Archie’s mother thanked them for their support.
“Thank you so, so much for supporting us while we were in that awful place,” she said.
“I hope you all stand by me in trying to change this law, Archie’s army, so that no more of our children and their parents go through this.”
Scores of purple balloons were then released into the air.
Earlier in the evening, Hollie spoke to the press.
Asked how the last few months have been, she said: “It’s been really hard. It was a fight for my little boy’s life.
“If I had to go back and do it again I would fight equally as hard.
“I will continue this fight. I have got no intention of giving up, Archie wouldn’t want me to give up, he would definitely want me to continue.
“Things have got to change.”
Ms Dance said that Archie’s religious beliefs should have been taken into consideration.
“Archie’s beliefs and Archie’s religion, what Archie would have wanted, just wasn’t taken into account – it was just brushed under the carpet,” she said.
Archie died on August 6 in the Royal London Hospital in Whitechapel, east London, after weeks of legal wrangling.
He had been in a coma since he was found unconscious by his mother at his home in Southend, Essex, on April 7.
He was being kept alive by a combination of medical interventions, including ventilation and drug treatments.
Doctors treating him for the last four months declared Archie to be “brain-stem dead”, prompting a lengthy legal battle by his family to continue his life support treatment in the hope he would recover.